Use of Fluorescent Protein in Studying Protein Half-Life

How long a protein remains in cell and at what equilibrium level depends on several factors: 1) how fast it is translated; 2) how fast it is degraded; 3) how much dilution by cell division affects its balance. A good method for tracking protein degradation requires live cell measurement methods that show high resolution because the changes may be small and gradual; and that do not interfere with cellular processes. One simple method was recently described in Science by Eden et al. that relies on bleaching fluorescent protein (FP) tagged to cellular protein of interest.

To track protein half-life, only a small fraction of FP is bleached with a pulse of light that would irreversibly damage the chromophore of the FP. This treatment, called bleach chase, would produce a population of proteins that are non-fluorescent and cannot be replenished. By comparing the fluorescence of this population and the control, unbleached population, it is possible to determine the half-life of the fused proteins using equation T1/2=ln(2)/a, where a is the slope of decay of the difference between bleached and unbleached protein fluorescence on a semilogarithmic plot. (This part is recited from AlleleNews)

Conversely, instead of photobleaching a FP to create a protein population, a fluorescent signal can be created and chased by photoactivating a photoactivable FP that is fused to a cellular protein under study. Plachta et al. published in a recent issue of Nature Cell Biology that by following the half-life, or kinetics of pluripotency-related transcription factor Oct4, cell fates are predicted in early embryo development.

In fact, there is a third method, perhaps soon to be published, that a photoconvertible FP can be used for tracking fusion protein half life. By using a photoconvertible FP, such as mClavGR (already offered by Allele), a fluorescent protein population can be created as in the aforementioned studies; but unlike bleaching or photoactivating, photoconversion keeps both populations (converted and unconverted, green or red in the case of mClavGR) present. This way all readings can be internally controlled to compensate for factors not directly related to protein metabolism per se, such as cell death, equipment variation, etc.

New Product of the Week 0201411-022111: Relaunch of Orbigen Apoptosis polyclonal antibodies on the new Allele online shopping system

Promotion of the week 021311-022111: This week save 10% on all custom viral services.

Tags: bleach chase, cell fate, mClavGR, Oct4 kinetics, photoactivable FP, photoconvertible FP, protein half life, pulse chase, YFP

New Frontiers for Research Tool Development in the New Year

Allele Biotech's Green Crystal Ball

Optogenetics
Chosen as the Method of the Year 2010 by Nature Method and mentioned in a number of year-end recaps, this is a technology that allows the use of light to precisely (at least in a temporal sense) control engineered proteins within a targeted cell population. For example, by introducing light-activated channelrhodopsins into neurons, one can use a pulse of light to initiate a movement of ion across the cell membrane. The technology, first reported in 2005 then made headlines as a major impact on neurosciences since 2007, is now being combined with other components in controlling a broader array of biological events, such as DNA binding, enzyme activities, etc. Looking forward, a few areas will be more than likely the frontlines of moving optogenetics into more labs:

Additional combinations: The few known channelrhodopsins and their fast growing variations will be combined with more “effecter” domains to control different events. The challenge will be to find ways to use the structural changes or any responses channelrhodopsins have to stimulating lights in order to trigger a reaction in the associated effecter domain.

Tracking mechanisms: A platter of fluorescent proteins (FPs) will be used as an independent tracking method to follow cells being targeted. FPs that have optical spectra that do not interfere with the optogenetic molecules will be tested and established. In addition, FPs with less toxicity, narrower excitation and emission peaks, and more tolerance to different cellular environment will be preferred and eventually set up as standards.

Delivery tools: To bring the optogenetic reagents into cells like neurons researchers will most likely rely on lentiviral vectors in most cases. Other vehicles such as baculovirus, MMLV-based retrovirus, even herpes virus may find broader applications in this field. Pre-packaged lentiviruses and MMLV-retroviruses already contain optogenetic constructs will become popular products.

VHH Antibodies
The small capture polypeptides based on single-domain Camelid antibodies (nanobodies, nano antbodies or nAbs) and similar VHH domains will become much dramatically more popular this year, judging from the significant increase in demands of the only camelid reagent products, GFP-Trap and RFP-Trap, in 2010. There are a number of NIH initiated programs that aim to find capture reagents that eventually target the complete human proteome. One of the key criteria for the current phase of the relevant NIH Director’s Initiative is ability to co-immunoprecipitate. The Human Proteome Organization (HUPO) recently expressed frustration due to the lack of high quality capture reagents necessary to isolate and identify most proteins. HUPO promotes global research on proteins in order to decode the human proteome. From what we have learned from dozens of publications showing the use of GFP-Trap, VHH molecules pulls down GFP-tagged proteins with unprecedented efficiency and purity. VHH antibodies show strong affinity and specificity, at a level superior or comparable to monoclonal antibodies. In addition, VHH antibodies are increasingly appreciated for their capabilities to recognize concave epitopes by their relatively convex-shaped paratopes. VHH nanobodies are small (~12-15 kD), with a limited number of functionally important disulfide bonds, can be expressed very well in E. coli, and are amazingly stable in extreme denaturing conditions such as heat and acid. They have been shown to be better suited for in vivo and trans-cellular membrane delivery than other antibodies. It should not be surprising that one day in the coming years VHH antibodies will be more dominant than monoclonal antibodies.

Super-Resolution Imaging
One of the goals of developing technologies such as photoactivated localization microscopy (PALM) and related super-resolution imaging (SRI) techniques was to achieve electron microscopy (EM) level resolution without using EM. Now new developments show that maybe combining EM and photoactivable FPs would provide more specific and more detailed morphology. It would be anticipated that more photoconvertible FPs will prove to work well for one type of SRI or another. The event that will bring this technology to nearly every cell biology lab is the improvement and availability of necessary instruments that some companies have already begun to commercialize.

New Product of the Week 010311-010911:

Human let-7b miRNA minigene on lentivirus with RFP reporter, ABP-RP-MILT7BLP

Promotion of the Week 010311-010911:

15% off mWasabi-based organelle markers carried on baculo2mammalian system if order this week (On-Demand products will require about 3-4 weeks for virus packaging after an order is placed). Use code 0103BACFP on fax or email order.

Tags: alpaca antibodies, camelid antibodies, channelrhodopsin, EM, halorhodopsin, optogenetic, PALM, photoactivable FP, photoconvertible FP, STED, STORM, VHH, VHH antibodies

Many Thanks to Give

We would like to thank our customers for choosing Allele’s products and services. The economic conditions have been challenging for the last two years and are still difficult. Allele Biotech could not have possibly achieved what it has within this time period without the support of its customers.

We thank online readers who visit our Blogs, News and Technical Forum to make our webpage one of the highest ranked among biology reagent suppliers; surpassing Clontech, Stratagene, Promega, IDT, etc. (by online ranking service Alexa’s accounts).

We thank our collaborators (some converted from customers) and business partners (manufacturers, distributors, licensors) for working with Allele and making our plan of one new product per week a reality. Allele Biotech has a very innovative and able research team, but working with researchers outside of the company is always a major part of the R&D effort at Allele.

Allele Biotech is obliged to its employees for their creativity, organization, dedication, and professionalism. The culture that they have nurtured here is to be individually motivated as a basic research group, and to be disciplined and organized as a service provider at the same time.

Allele Biotech is a beneficiary of the US government’s policies on supporting biomedical research and innovation. We appreciate the support for our basic research in the forms of grants and contracts from the NIH and the IRS, and ultimately the American tax payers. It is our duty to create and produce better tools for improving human health.

Thank you once again and have a Happy Holiday!

New Product of the Week 112210-112810:

Photoconvertible FP mClavGR (green-to-red) on lentiviral vector pLICO, email FP@allelebiotech.com for product details.

Promotion of the Wee 112210-112810:

10% additional discount off HPLC siRNA’s promotion price, $135/15 nmol, use promo code FB112210si, order by emailing oligo@allelebiotech.com.

Tags: Clontech, collaboration, collaborators, customer opinions, customer service, IDT DNA, IDT oligo, Life Technologies, mClavGR, photoconvertible FP, promega, Stratagene, thanksgiving